The major problem is the rape myth.

"For men, physical arousal and the desire to have sex are closely connected, but women can be ‘physically aroused’ (with increased blood flowing to the reproductive organs) but still not interested in having sex.  "

No, a man can be physically aroused and have no interest in having sex as well. An erection <> consent. What makes it worse is that they even point this out in the article.

"There are documented cases where one pill has produced an agonising ten-hour erection which just doesn’t go down "

Of course women have to able to control everything. That's just standard fare in articles today.

"what’s the etiquette here: should he always ask before he takes one? "

Only if she loses the right to revoke consent after he takes one, otherwise it doesn't concern her any more than fake boobs or hair extension affect a man. It's not like contraception, which if she's not taking it or taking it improperly, could affect him. If she doesn't want to have sex at any time, she doesn't have to.

http://archive.is/B3mC0